I'm hoping someone can help me out here. I'm attempting bluecrab's mod. I bought a Mode Electronics jack (part 24-391-1):
My problem is that I have no idea how to wire the jack and I can't find any diagrams online. Anyone familiar with these?

I'm hoping someone can help me out here. I'm attempting bluecrab's mod. I bought a Mode Electronics jack (part 24-391-1):
My problem is that I have no idea how to wire the jack and I can't find any diagrams online. Anyone familiar with these?

You'd have to probably get an ohm meter and take a plug and cut and strip the wires, then do some plugging in and measuring.

This switch has 2 sets of contacts, as described in the following pdf as having "2 normally closed switches", kinda like a double throw switch in a way. It looks like the Sena output would go to pins 2 and 5, and normally 2 & 5 are connected to pins 3 & 4 (helmet speakers?). Then when you plug in your earbuds it connects pins 2 & 5 to the earbud wires. You have to figure out polarity which is which.

I also modified the factory earbud clamp to use the audio input jack for the "full stereo" mode. I can still use the original output jack for the "no noise mono" mode. After riding for couple of weeks, I prefer good stereo even with the background buzz. The buzz is masked by the engine sound even on idle, but audio quality is considerably better. That mode is simple, just cut 3 traces and solder 2 jumpers.]

I did this mod the other day using the method outlined by TXjames, it works great, great stereo, no buzz and a jack that will long outlive that crappy afterthough extendo jack.

Thanks to all who posted data on this mod.

Quote:

Originally Posted by TXjames

Excellent post genka!
My buddy approached it a bit differently by replacing the output and relocating it to the bottom of the baseplate. He did an excellent repair but I was stuck on the same idea that genka had.

I simply reused the broken wires

and jumpered the normal output to the appropriate sides on the fixed audio jack. However, I did replace the ground with a shielded wire.

Note that the right channel is not visible because it's under the ground wire. And I didn't have to add the 75 Ω resistors because they were already there.

Fortunately, I found this thread before attacking. Already knowing which traces to cut (to keep from shorting the aux in with the earbud out) saved me some time.

My observations of repurposing the aux in as the earbud output:
1. It's difficult to locate the new output in everyday use; with the baseplate mounted to the side of your head and motorcycle gloves on.
2. The microphone wire needs to be routed with attention so that it does not get in the way while plugging in the headphones.

__________________"If you can't be kind, at least have the decency to be vague."

Is it possible OP has miswired his headset? I'm an electrical engineer....

If R+, R-, L+ and L- are what they intuitively seem to be, then...

OP has added an unwanted resistance between the right and left channels, which will damage the stereo sound, make it sound flat, all the things a later poster describes. (Properly mis-wired, it may even effectively remove vocals from stereo recordings...)

I'd like the chance to discuss this, if OP is still around.

If it's truly 3-wire, R+, L+, and Common, then a resistor between R+ and C, and another between L+ and C would make more sense.

It's quite possible I'm missing something with all the cut traces, etc, as I cannot / will not attempt to create a schematic from someone else's circuit from pictures on the internet... of a circuit board for which I also have no schematic.

If it were MY headset I would have tried wiring a 7.5 ohm between R+ and R-, and another one between L+ and L-.

7.5, not 75. Could that be another mistake by OP? A 75 ohm resistor placed in parallel with a 2-4 ohm earbud speaker's going to have next to zero effect. Its like placing a garden hose next to an irrigation canal.

One could simply put a 1-10 ohm (exact level TBD) resistor IN LINE with the common lead if it's a 3-wire headphone circuit. Much simpler.

Your attempt to FORCE their circuit board to accept a 3-wire headset cord is where the problem lies, not with Sena's design. In fact their dual amplifier 4-wire design will provide MUCH better stereo sound, separation, and ESPECIALLY VOLUME....

The solution is to sever your earbud cord where it splits into two separate wires, and HARD wire those to the circuit board, or else use two mono jacks, instead of trying to force a 3-wire cord onto a pair of differential amps.

OP is to be commended for trailblazing, readers are commended for reading down this far in the thread to find out how to do it correctly.

Cheers!

__________________
The only possible explanation is that God Himself loves road trips, and watches over those who take them.a

There is one mistake in the wiring, it switches left and right channels- which doesn't really affect anything.

Quote:

If it's truly 3-wire, R+, L+, and Common, then a resistor between R+ and C, and another between L+ and C would make more sense.

It's quite possible I'm missing something with all the cut traces, etc, as I cannot / will not attempt to create a schematic from someone else's circuit from pictures on the internet... of a circuit board for which I also have no schematic.

If it were MY headset I would have tried wiring a 7.5 ohm between R+ and R-, and another one between L+ and L-.

7.5, not 75. Could that be another mistake by OP? A 75 ohm resistor placed in parallel with a 2-4 ohm earbud speaker's going to have next to zero effect. Its like placing a garden hose next to an irrigation canal.

The resistors are in series with the earbuds. They are needed because earbuds work at lower power levels compared to the helmet speakers. Although other users reported that connecting the earbuds directly is not overly loud and acceptable. Sena's own earbud clamp uses 75 Ohm resistors.

Quote:

If it were MY headset I would have tried wiring a 7.5 ohm between R+ and R-, and another one between L+ and L-.

7.5, not 75. Could that be another mistake by OP? A 75 ohm resistor placed in parallel with a 2-4 ohm earbud speaker's going to have next to zero effect. Its like placing a garden hose next to an irrigation canal.

Not even sure what are you trying to accomplish here. The goal of my mod was to convert the helmet speaker clamp for exclusive earbud use.

Quote:

One could simply put a 1-10 ohm (exact level TBD) resistor IN LINE with the common lead if it's a 3-wire headphone circuit. Much simpler.

Completely wrong, it is never done this way. Such circuit would introduce a crosstalk.

Your attempt to FORCE their circuit board to accept a 3-wire headset cord is where the problem lies, not with Sena's design. In fact their dual amplifier 4-wire design will provide MUCH better stereo sound, separation, and ESPECIALLY VOLUME....

Umm, Yes.
I essentially duplicated the circuitry Sena uses in the earbud clamp they sell. It also uses one of the "-" leads as a common for the 3 wire system and suffers from exactly the same problem of poor channel separation. I had an extensive e-mail discussion with Sena, and they agreed that it is an inherent design flow. They added the earbud clamp as an afterthought. The 4 wire system is great, but it only works with speakers.

Quote:

The solution is to sever your earbud cord where it splits into two separate wires, and HARD wire those to the circuit board, or else use two mono jacks, instead of trying to force a 3-wire cord onto a pair of differential amps.

I thought about it, and saw no practical way to get it working reliably. First of all, in most cases earbuds can't be converted to a 4 wire circuit. After the L and R wires joint together the common wire has 3 conductors. You could buy 2 pairs of earbuds and cut off one bud from each. Also you need to install another 3.5mm jack in the clamp, and there is not enough room to do it. You can dangle it outside- not a neat and reliable solution.

Originally Posted by bobframe
If you tire of doing this yourself or are intimidated to begin....

You might give Marilyn at Plug Up a call. A friend had her replace the factory speakers with a headphone jack so he could use his own headphones and he reports great results. She has done a bit of work for me...repairing a pair of custom ear phones...reasonably priced and quick.

Marilyn does have great stuff!
She had a booth at Laguna last year. I really wanted the molded plugs but was poor, ( still am !) so I got the S-plug instead, basically a sillicone rubber plug with minispeakers. The sound quality is AMAZING. deep, rich bass and clear mid-high tones. Love it. Gripes? The white wiring gets dirty quick - it has a slightly rough surface that allows dirt to imbed.

'Installing' the plugs requires a solid tug at your earlobe and the plug has to be really shoved deep into the ear canal, otherwise it tends to dislodge. Once in, ambient wind-noise is almost nil. Love it!

You seem to have an overriding goal of being able to plug standard earbuds into a stereo mini-jack contained in the Sena unit. I don't. My goal is best quality sound, stereo separation, AND significantly more volume.

So I'm not using a jack, and no 4-to-3 wire conversion is needed. I've hardwired my earbuds, 2 wires each.

thanks for the tip on Sena using a 75 ohm shunt. I'll try a 47 ohm for slightly greater volume.

I really like your idea of cobbling two sets of earbuds into one. Heck, I could mount two minijacks into the side of the helmet itself so I could rapidly unplug when someone starts talking and I need to hear:

"Yes officer, I can hear you just fine..."

Again, you pioneered this, led everyone down the road and deserve kudos, even though our audio goals differ. Readers can decide for themselves between the flexibility of wiring up a standard jack plug-in versus highest quality sound.

W

__________________
The only possible explanation is that God Himself loves road trips, and watches over those who take them.a

You seem to have an overriding goal of being able to plug standard earbuds into a stereo mini-jack contained in the Sena unit. I don't. My goal is best quality sound, stereo separation, AND significantly more volume.

I'm with genka.

If I want the best quality sound, I won't be using a motorcycle helmet as the platform for my sound stage.

You seem to have an overriding goal of being able to plug standard earbuds into a stereo mini-jack contained in the Sena unit. I don't. My goal is best quality sound, stereo separation, AND significantly more volume.

So I'm not using a jack, and no 4-to-3 wire conversion is needed. I've hardwired my earbuds, 2 wires each.

Although I listen to audiobooks more often than I do to music, I'd love to have a good stereo separation. Still, on a bike I prefer a more reliable setup. Leaving the jack allows me to swap the earbuds when I have to or disconnect them completely.
And keep in mind that raising the power to the earbuds will make that load beep Sena makes when reaching the maximum volume even louder.

No resistor was required. At maximum volume on the Sena there was no distortion or overload; no reason to add a resistor. I simply cut off the speakers and wired the two earbuds right in. Suggest you leave as much wire as possible connected to the Sena, short as possible to the speakers unless you plan to re-use / sell the speakers.

The earbud wires have either a clear or a colored varnish on them. Scraping didn't do a good job of removing it; a little heat from a cigarette lighter did, prior to attempting to solder them.

You have to be pretty good at soldering to do work this tiny. Don't forget to put the heat shrink tubing on BEFORE you solder the wires...

Note, I did a 4-wire conversion. My earbuds DO NOT unplug from the helmet. I get maximum volume AND stereo separation by doing it this way.

Putting the helmet on is a challenge. I have to set it on a countertop of some sort, insert the earbuds, then pull the helmet over without knocking 'em out. Longer wires would make it a LOT easier.

If I was going to do it over, I would do what OP suggested in his last post, get TWO sets of earbuds, cut the right out of one, the left out of the other, and use TWO mini-jacks to plug in. You'd get full stereo separation, full volume, more cable length, AND the ability to plug/unplug / replace headphones.

__________________
The only possible explanation is that God Himself loves road trips, and watches over those who take them.a